Relative vs Absolute Risk: Two Ways to Read One Result
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Relative vs absolute risk

Also called relative risk, absolute risk, risk ratio, RR, risk difference · Reviewed

Definition: Relative risk compares the risk of an event in one group with the risk in another; the NCI says a relative risk of 1 means no difference. Absolute risk is the chance of the event itself over a set time. The same trial result can be stated both ways, and labels often print both.

A worked example from a label

WHI invasive breast cancer, as printed on the Bijuva label

  1. Women on estrogen plus progestin: 43 cases per 10,000 women-years. On placebo: 35 per 10,000 women-years.
  2. Relative risk: the label prints 1.24, about a quarter higher. (43 ÷ 35 is about 1.23; the label works from the unrounded data.)
  3. Absolute difference: 43 − 35 = 8 more cases per 10,000 women-years.
  4. Both lines describe the same trial result.

Another example

On the Evenity label, major heart events against alendronate were 2.0% vs 1.1%. The hazard ratio was 1.87, close to double, while the absolute gap was 0.9 percentage points. The NCI notes that relative risk is used in studies that follow people forward, such as cohort studies and clinical trials. Its own example of absolute risk: a 35-year-old woman with no known risk factors has about a 13% chance, or 1 in 8, of breast cancer over a lifetime to age 90.

Why it matters for your log

A relative number alone can sound larger or smaller than the absolute change behind it. When you read a risk on a label or in a headline, look for both, and bring both to your prescriber.

Read more on Dose Track: Bijuva side effects · Evenity side effects · Bijuva vs Prometrium · Side effects from FDA labels

General education drawn from labels and published studies, not personal medical advice. Your prescriber, pharmacist and the label that came with your product are the final word.
Hazard ratioA hazard ratio (HR) compares how often an event happens over time in one group with how often it happens… Meta-analysisA meta-analysis is an analysis that combines data from several studies on the same subject. The NCI says… Women's Health InitiativeThe Women's Health Initiative (WHI) is a large set of studies in postmenopausal women aged 50 to 79 that… PlaceboA placebo is an inactive substance or other treatment that looks the same as, and is given the same way…

Frequently asked questions

What is the difference between relative and absolute risk?+
Relative risk compares two groups, such as 1.24 times the rate. Absolute risk is the chance itself, such as 43 cases per 10,000 women-years. The gap between groups (8 per 10,000 women-years in that example) is the absolute difference.
What does a relative risk of 1 mean?+
The NCI says a relative risk of 1 means there is no difference between the two groups.

Sources

  1. NCI Dictionary of Cancer Terms: relative risk
  2. NCI Dictionary of Cancer Terms: absolute risk
  3. Bijuva (estradiol and progesterone) US prescribing information, DailyMed
  4. Evenity (romosozumab-aqqg) US prescribing information, DailyMed

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